In the related art, there is a lamp unit using a cap of GX53 type. The lamp unit of this type includes a disk-shaped base member. A light source is arranged on one surface side of the base member, the cap is arranged on the other surface side, and a lighting circuit is arranged between the base member and the cap.
The cap is formed with a cap surface portion in a peripheral portion of the other surface and is formed with a cap projection at a center portion of the other surface so as to project from the other surface side of the cap surface portion and having an interior opening toward the one surface side, and is provided with a pair of lamp pins projecting from the other surface side of the cap surface portion.
The lighting circuit includes a lighting circuit substrate and a plurality of lighting circuit components mounted on the lighting circuit substrate, and both of the lighting circuit substrate and the lighting circuit components are arranged within the cap projection.
The above mentioned technology is disclosed in Japanese Patent Application Laid-Open No. 2011-171160, and contents of which are hereby incorporated by reference.